Gran Turismo 4 and its not even close. I've stated before that I'm a racer at heart, I'm also a sucker for simulators. GT4 is considered a type of simulator by many because it does accurately mirror real time racing. The amount of cars available in the game is flat out ridiculous, they have everything from muscle cars to sport cars to supercars even old classic cars like the Model T and the Silverghost are in this game. The tracks vary from road courses off of a Las Vegas highway to a track at Le Mans to a track from Indycar. The game had endless amounts of replay value, with the multiplayer mode just adding to the fun.
I remember playing Fable, many of my friends enjoyed the game, I however got bored of it rather quickly. Never really been too big on RPG's in general, yeah there are a few that I enjoyed, but Fable wasn't one of them. This is the reason why I never got swept up in the World of Warcraft craze either.